Put the chopped onion, garlic and carrot into a large microwave safe bowl.
Add the mince and mix together with a fork, breaking up the meat until it is well combined.
Cover the bowl with a microwaveable lid or cling film, leaving a small area open, and microwave on full power for three minutes.
Remove the bowl. Stir with the fork, breaking up the mince again, cover and return to the microwave for another three minutes. Take care when removing the bowl as it will be very hot. Break up any clumps of mince again.
Add the chopped tomatoes to the bowl together with 50ml/2fl oz of boiling water, and crumble over the stock cube, oregano and black pepper (if using).
Mix everything together with a wooden spoon. Cover again and cook in the microwave on full power for seven minutes. Remove the bowl, stir well, cover and return to the microwave for another 10 minutes on full power, stirring halfway through.
Remove the bowl and leave to stand while you cook the spaghetti.
Boil the kettle for the spaghetti. Break the spaghetti into thirds and put in a separate microwave safe bowl. Add the oil and mix well with a wooden spoon to coat the spaghetti with oil. Pour over boiling water until just covered and stir well.
Put into the microwave and cook on full power for four minutes.
Remove the bowl and stir the spaghetti. Cover and return to the microwave and cook on full power for another four minutes.
Take the bowl out of the microwave and leave to stand for two minutes. Check that the spaghetti is cooked and is al dente (still has a little bite). Cook for another couple of minutes if it’s not soft enough.
Drain the cooked spaghetti and serve with the bolognese sauce.